For instance, for this website - webconfs.com we could try optimizing for the keyword "Search Engine Optimization". It could take a year or so with a LOT of effort to reach the first page on Google for "Search Engine Optimization” and still one can never be sure this will happen.
However, let's pretend that this happens – We manage to top Google for "Search Engine Optimization” after a year of hard SEO work. To our greatest disappointment, even the first place for "Search Engine Optimization” on Google did'nt bring the expected results because the bounce rate for this particular keyword turned out to be very high. Since we do not provide SEO Services a lot of people reaching us via "Search Engine Optimization" may NOT be getting what they're looking for. Instead, lesser popular keywords, such as "SEO Tips” or "SEO Guide” might have lower bounce rates and may actually perform better than "Search Engine Optimization” did for us.
The result is not surprising but the price paid is. If we had launched an AdWords campaign, it would have saved a lot of trouble. We could have spent $20-50 on AdWords for "Search Engine Optimization” and it would have taken us a week or less to figure that the bounce rate for this keyword is very high and it makes no sense to do organic SEO for it. These $20-50 on AdWords would have spared a year of wasted SEO efforts.